The polymerization of silicic acid in dilute aqueous solutions



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The polymerization of silicic acid. and. its relationship to natural systems has been of interest to chemists and. geologists for almost a hundred years. Although a large amount of work has been done on aqueous solutions of relatively high concentrations of silicic acid, little has been done on silica solutions approaching the concentration ranges found in natural waters. In an attempt to observe the polymerization reactions of silicic acid on a molecular basis, a series of reaction systems at a constant initial silica concentration and variable concentrations of chloride and perchlorate were followed for a period of 200 hours. The rate data showed a definite second order nature in the initial portion of the reaction and the forward rate constants were calculated for this region. A mechanism has been proposed for the polymerization process which involves the formation of a hydrogen bonded species as a pre-equilibrium step. The presence of chloride ion in the polymerizing solution has a much greater effect than would be expected from just an ionic strength effect. A mechanism for the reaction of the chloride ion with silicic acid has also been proposed.